Panel and a liquid crystal display including the panel

ABSTRACT

An LCD according to the present invention includes lower and upper panels facing each other and a liquid crystal layer interposed therebetween. The upper panel includes a black matrix formed on an inner surface of an insulating substrate, having openings corresponding to pixel areas, and blocking the light leakage between the pixel areas, a plurality of red, green, and blue color filter sequentially arranged in the pixel regions, a flat layer formed on the red, green and blue color filters, and a common electrode formed on the flat layer, made of transparent conductive material such as ITO (indium tin oxide) or IZO (indium zinc oxide), and supplied with a predetermined voltage for driving the liquid molecules in cooperation with the pixel electrodes. In addition, a light diffraction layer having micro structure of slit pattern or diffraction lattice is formed between the black matrix and the red, green, or blue color filters. The light diffraction layer is made of transparent conductive material such as ITO or IZO or transparent insulating material such as silicon nitride or silicon oxide. The gap between the slits or width of slits of the light diffraction layer is preferably equal to or less than seven microns and it is possible to have two or more different widths or gaps in the range of equal to or less than 7 microns.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a panel and a liquid crystal displayincluding a panel, and in particular, to a panel including lightdiffraction layer and a liquid crystal display including the panel.

(b) Description of Related Art

A liquid crystal display (LCD) includes a lower panel provided with thinfilm transistors (TFTs), etc., an upper panel provided with colorfilters and a black matrix, etc., and a liquid crystal layer interposedtherebetween. A plurality of pixel electrodes and a common electrode areformed on the respective panels or on a single panel and supplied withvoltages. The LCD varies the voltages applied to the pixel electrodesand the common electrode to change the orientations of liquid crystalmolecules. In this way, the LCD adjust the transmittance of light anddisplays images.

The liquid crystal material of an LCD has birefringence that therefractive indices in a direction of molecular long axes and in adirection of molecular short axes are different from each other. Due tothe birefringence, the refractive index which the light experiencesdepends on the viewing direction of the LCD, and this differentiates thepolarization of an incident light with linear polarization after passingthrough the liquid crystal. Therefore, the color characteristic and theamount of the light in a slanted direction are different from those in afront direction. In particular, a twisted nematic (TN) LCD sufferssevere problems such as the contrast ratio depending on the viewingangle, color shift, gray inversion, etc., due to the variation of theretardation of the light.

A technique for solving these problems is developed, which compensatesthe phase difference in a specific direction using phase differencecompensation film. This technique is to solve the viewing angle problemby compensating the phase deviation of the light generated by the liquidcrystal in an opposite manner using the compensation films. Then, theviewing angle is ensured in twisted nematic type LCD using the phasedifference compensation films, however, the gray inversion in lowerviewing angle, etc., still remains.

SUMMARY OF THE INVENTION

A motivation of the present invention is to provide an LCD capable ofminimizing the gray inversion.

According to the motivation, a light diffraction layer having a slitpattern or a diffraction lattice is formed on a panel for an LCD of thepresent invention.

Here, the panel may include a black matrix having openings on pixelareas and red, green, and blue color filters formed on the pixel areasand arranged in sequence, and the light diffraction layer is preferablydisposed between the black matrix and the red, green, and blue colorfilters.

Moreover, it is preferable that width and interval of the slit patternare equal to or less than seven microns, and width and interval of theslit pattern may be uniform in each pixel area or may have at least twodifferent values in each pixel area. Preferably, the light diffractionlayer is made of transparent conductive material or transparentinsulating material.

An LCD according to the present invention includes the above-mentionedpanel, an additional panel facing the panel and a liquid crystal layerinterposed between the two panels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a layout view of an LCD according to an embodiment of thepresent invention;

FIG. 2 is a sectional view of an LCD shown in FIG. 1 taken along theline II-II′;

FIG. 3 is a graph showing the luminance for a plurality of grays asfunction of the viewing angle in a lower vertical direction of an LCDwithout a light diffraction layer;

FIGS. 4A and 4B are graphs showing the luminance for a plurality ofgrays as function of the viewing angle in the lower vertical directionof LCDs including light diffraction layers with a slit pattern A;

FIGS. 5A and 5B are graphs showing the luminance for a plurality ofgrays as function of the viewing angle in the lower vertical directionof LCDs including light diffraction layers with a slit pattern B;

FIGS. 6A and 6B are graphs showing the luminance for a plurality ofgrays as function of the viewing angle in the lower vertical directionof LCDs including light diffraction layers with a slit pattern C;

FIGS. 7A and 7B are graphs showing the luminance for a plurality ofgrays as function of the viewing angle in the lower vertical directionof LCDs including light diffraction layers with a slit pattern D;

FIGS. 8A and 8B are graphs showing the measured contrast ratio asfunction of the viewing angle in the vertical direction of LCDsincluding light diffraction layers with the slit pattern A;

FIGS. 9A and 9B are graphs showing the measured contrast ratio asfunction of the viewing angle in the vertical direction of LCDsincluding light diffraction layers with the slit pattern B;

FIGS. 10A and 10B are graphs showing the measured contrast ratio asfunction of the viewing angle in the vertical direction of LCDsincluding light diffraction layers with the slit pattern C; and

FIGS. 11A and 11B are graphs showing the measured contrast ratio asfunction of the viewing angle in the vertical direction of LCDsincluding light diffraction layers with the slit pattern D.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein.

In the drawings, the thickness of layers and regions are exaggerated forclarity. Like numerals refer to like elements throughout. It will beunderstood that when an element such as a layer, film, region, substrateor panel is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present. Then, acolor filter panel, a transflective liquid crystal display, and amanufacturing method thereof according to embodiments of the presentinvention will be described with reference to the drawings.

Now, thin film transistor array panels and LCDs including panelsaccording to embodiments of the present invention are described indetail with reference to the accompanying drawings.

FIG. 1 is a layout view of an LCD according to an embodiment of thepresent invention, and FIG. 2 is a sectional view of an LCD shown inFIG. 1 taken along the line II-II′.

As shown in FIG. 1, an LCD according to an embodiment of the presentinvention includes lower and upper panels 100 and 200 facing each otherand a liquid crystal layer 300 interposed therebetween. The dielectricanisotropy Δε of the liquid crystal layer 300 is larger than zero.Liquid crystal molecules in the liquid crystal layer 300 have a twistednematic configuration that the long axes of the liquid crystal moleculesare parallel to the surfaces of the panels 100 and 200 and spirallytwisted from one panel to the other in absence of electric field, andthe liquid crystal molecules are oriented under application of electricfield with a sufficient strength to the liquid crystal layer 300 suchthat long axes of the liquid crystal molecules are perpendicular to thesurfaces of the panels 100 and 200 and parallel to the electric field.

The lower panel 100 includes a plurality of pixel electrodes forperforming display operation formed on pixel areas arranged in a matrix,a plurality of gate lines and a plurality of data lines intersectingeach other to define the pixel areas and transferring scanning signalsand image signals, respectively, a plurality of TFTs electricallyconnected to the gate lines and the data lines and controlling the imagesignals from the data lines in response to the scanning signals from thegate lines, etc. The lower panel 100 is called TFT array panel.

The upper panel 200 includes a black matrix 220 formed on an innersurface of an insulating substrate 210, having openings corresponding tothe pixel areas, and blocking the light leakage between the pixel areas,a plurality of red, green, and blue color filters 230 sequentiallyarranged in the pixel regions, a flat layer 250 formed on the red,green, and blue color filters 230, and a common electrode 270 formed onthe flat layer 250, made of transparent conductive material such as ITO(indium tin oxide) or IZO (indium zinc oxide), and supplied with apredetermined voltage for driving the liquid molecules in cooperationwith the pixel electrodes. In addition, a light diffraction layer 260having micro structure of slit pattern or diffraction lattice is formedbetween the black matrix 220 and the red, green, or blue color filters230. The light diffraction layer 260 is made of transparent conductivematerial such as ITO or IZO or transparent insulating material such assilicon nitride or silicon oxide. The gap between the slits or width ofslits of the light diffraction layer 260 is preferably equal to or lessthan seven microns and it is possible to have two or more differentwidths or gaps in the range of equal to or less than 7 microns.Moreover, although the slits of the light diffraction layer 260 extendin a horizontal direction, the slits may extend in a vertical directionor a diagonal direction based on a direction in which the gray inversionis required to be minimized according to the viewing angle. The lightdiffraction layer 260 including the slits extending in horizontaldirection has a function of equalizing the light by diffracting thelight passing through the liquid crystal layer 300 in the verticaldirection, thereby improving the gray inversion in the lower direction.This is described in detail with reference to the experimental examplesand drawings.

The light diffraction layer 260 may be formed of a polymer dispersedliquid crystal layer or an organic layer having an embossed surface.Alternatively, it includes minute particles for diffracting the light.

Here, although the red, green, and blue color filters 230 are separatedon the black matrix 220, two or more color filters 230 may overlap eachother. Polarizers may be attached to outer surfaces of the two panels100 and 200, which can polarize the light passing through the liquidcrystal cell 100, 200, and 300, and transmission axes of the polarizersattached to the outer surfaces of the two panels 100 and 200 areparallel to or perpendicular to each other.

Here, the liquid crystal layer 300 is in a VA (vertically aligned) modeand has negative dielectric anisotropy. The liquid crystal moleculesaligned substantially perpendicular to the panels 100 and 200 arealigned substantially parallel to the panels to the mid-plane of the twopanels 100 and 200 upon application of sufficient voltages. A PVA(patterned vertically aligned) mode LCD including cutouts as domaindividing members provides a plurality of cutouts for the pixelelectrodes and/or the common electrode, and cutouts of the pixelelectrodes and cutouts of the common electrode may divide the pixel areainto left and right domains and upper and lower domains.

Moreover, the liquid crystal layer 300 can have an alignmentconfiguration of HAN (hybrid aligned nematic) mode or OCB (opticallycompensated bend) mode. An OCB mode LCD includes alignment layers foraligning the liquid crystal molecules substantially parallel to thesurfaces of the panels 100 and 200 and substantially in a singledirection. The liquid crystal molecules are aligned symmetrical to amid-plane between the two panels and vary their orientations from ahorizontal alignment at the surfaces of the panels to vertical alignmenton the mid-plane of the two panels.

Next, experiments are described in detail with reference to theaccompanying drawing as mentioned above.

Experiments

Experiments utilized liquid crystal cells in twisted nematic mode. Alight diffraction layer 260 of ITO with thickness of about 1,200 Å orsilicon nitride with thickness of about 3,000 Å was formed between colorfilters and a black matrix, and the luminance for several gray asfunction of the viewing angle in a lower vertical direction and theviewing angles in a vertical direction were measured. Here, the figuresindicated by figure numbers including A show the cases that the lightdiffraction layer 260 is made of ITO, and those indicated by the figurenumbers including B show the cases that the light diffraction layer 260is made of silicon nitride. A slit pattern A is the case that the widthand the gap of the slits are 6.5 microns and 4.5 microns, respectively,a slit pattern B is the case that the width and the gap of the slits are5.0 microns and 3.25 microns, respectively, a slit pattern C is the casethat a pixel area is trisected and the widths and the intervals of theslits in the sections are 5.0 microns and 3.0 microns, 6.0 microns and4.0 microns, and 7.0 microns and 5.0 microns, respectively, and a slitpattern D is the case that a pixel area is bisected and the widths andthe intervals of the sections are 5.0 microns and 3.0 microns, and 7.0microns and 5.0 microns, respectively.

FIG. 3 is a graph showing the luminance for a plurality of grays asfunction of the viewing angle in a lower vertical direction of an LCDwithout a light diffraction layer, FIGS. 4A and 4B are graphs showingthe luminance for a plurality of grays as function of the viewing anglein the lower vertical direction of LCDs including light diffractionlayers with the slit pattern A, FIGS. 5A and 5B are graphs showing theluminance for a plurality of grays as function of the viewing angle inthe lower vertical direction of LCDs including light diffraction layerswith the slit pattern B, FIGS. 6A and 6B are graphs showing theluminance for a plurality of grays as function of the viewing angle inthe lower vertical direction of LCDs including light diffraction layerswith the slit pattern C, and FIGS. 7A and 7B are graphs showing theluminance for a plurality of grays as function of the viewing angle inthe lower vertical direction of LCDs including light diffraction layerswith the slit pattern D. In the figures, “1 Gray”, “10 Gray”, “19 Gray”,“28 Gray”, “37 Gray”, “46 Gray”, “55 Gray”, and “64 Gray” mean grays,-10, -20, -30, -40, -50, -60, -70, and -80 mean the values of theviewing angle in the lower direction. The gray inversion that theluminance of a lower gray is higher than that of a higher gray isindicated as hatched areas.

As shown in FIG. 3, severe gray inversion is shown from 40 to 70 degreesin the lower viewing angle if there is no light diffraction layer. Ifthe slit patterns A-D are applied, the gray inversion is drasticallydecreased as shown in FIGS. 4A to 7B although the gray inversion occursin the same range of the viewing angle as that shown FIG. 3.

Next, the viewing angle measured under the same condition will bedescribed.

FIGS. 8A and 8B are graphs showing the measured contrast ratio asfunction of the viewing angle in the vertical direction of LCDsincluding light diffraction layers with the slit pattern A, FIGS. 9A and9B are graphs showing the measured contrast ratio as function of theviewing angle in the vertical direction of LCDs including lightdiffraction layers with the slit pattern B, FIGS. 10A and 10B are graphsshowing the measured contrast ratio as function of the viewing angle inthe vertical direction of LCDs including light diffraction layers withthe slit pattern C, and FIGS. 11A and 11B are graphs showing themeasured contrast ratio as function of the viewing angle in the verticaldirection of LCDs including light diffraction layers with the slitpattern D.

While the measured upper viewing angle and the measured lower viewingangle giving the contrast ratio equal to ten were equal to 55 and 58degrees, respectively, when no light diffraction layer is applied, thosewere about 60 and 62 degrees, respectively, when the light diffractionlayers having the slit patterns A-D were applied as shown in FIGS. 8A to11B. Therefore, it can be known that the viewing angle is also increasedif a light diffraction layer having a slit pattern is applied.

Therefore, according to LCDs of the present invention, thecharacteristics of the display devices are improved by applying a lightdiffraction layer having a slit pattern or a diffraction lattice tominimize the gray inversion.

1. A first panel for a liquid crystal display, the panel comprising: aninsulating substrate; and a light diffraction layer formed on an innersurface or an outer surface of the substrate and having a slit patternor a diffraction lattice for diffracting light passing though an liquidcrystal layer.
 2. The panel of claim 1, further comprising a blackmatrix having a plurality of openings on pixel areas and red, green, andblue color filters formed on the pixel areas and arranged in sequence.3. The panel of claim 2, wherein the light diffraction layer is disposedbetween the black matrix and the red, green, and blue color filters. 4.The panel of claim 1, wherein width and interval of the slit pattern ofthe light diffraction layer are uniform in each pixel area.
 5. The panelof claim 1, wherein width and interval of the slit pattern of the lightdiffraction layer have at least two different values in each pixel area.6. The panel of claim 1, wherein the light diffraction layer comprisestransparent conductive material or transparent insulating material. 7.The panel of claim 1, wherein width and interval of the slit pattern ofthe light diffraction layer are equal to or less than seven microns. 8.A liquid crystal display comprising: first panel of any one of claims 1through 7; a second panel facing the first panel; and a liquid crystallayer interposed between the first panel and the second panel.